This invention relates to switching power supplies utilizing an inverter and, more particularly, to a switching power supply of the type which requires an accurately regulated low power source for the control and drive circuits of the power supply itself.
In switching power supplies, attention is usually directed toward improving the power stages such as the inverter and the input and output filter circuits to achieve improved performance and reliability. However, in order to control and drive the aforementioned components, low voltage regulated power at a plurality of levels must be generated. A common method of generating an internal power source utilizes a 60 Hz or line frequency power transformer followed by well-known rectifiers and series pass regulators which make up the usual internal bias supply. Generally, when a lightweight power supply is required, the 60 Hz transformer contributes a relatively large proportion of the power supply weight. Also, as is obvious, this transformer cannot be operated from a direct current supply voltage source which is often used in uninterrupted power systems backed up by a battery source. In addition, the transformer input taps must be changed with any change in AC line voltage, say from 115 to 230 volts AC line voltage. When it is desirable to use alternating or direct current as the original source, it becomes necessary to provide DC regulated low voltages obtained from the unregulated DC or rectified AC input power source. This low voltage source can be provided from a voltage divider or emitter follower circuit. However, these methods are extremely inefficient. The voltage divider produces a continuous current drain, and similar dissipation occurs in the emitter follower unless complex feedback and regulation from the main inverter is used.
It is, therefore, an object of the invention to provide an improved switching power supply which contains an efficient, lightweight and low cost regulated internal power supply system for the control and drive circuits of said power supply.
Another object of the invention is to provide a preregulated power supply having a drive and control circuit which is floating or isolated in a manner which permits direct coupling to the power switching regulator device without requiring isolating devices such as transformers or optical isolators.
Another object of the invention is to provide a plurality of regulated voltage levels which are completely isolated from either the power supply common input line or output line and which can be used to provide power to the reference control and inverter drive circuits within the supply.
A further object of the present invention is to provide an improved switching power supply having an internal power source or preregulator that is relatively compact, lightweight and highly efficient in use.